Re: [PATCH 6/8] KVM: SVM: Re-inject INTn instead of retrying the insn on "failure"

From: Maciej S. Szmigiero
Date: Mon Apr 04 2022 - 18:03:13 EST

On 2.04.2022 03:09, Sean Christopherson wrote:
Re-inject INTn software interrupts instead of retrying the instruction if
the CPU encountered an intercepted exception while vectoring the INTn,
e.g. if KVM intercepted a #PF when utilizing shadow paging. Retrying the
instruction is architecturally wrong e.g. will result in a spurious #DB
if there's a code breakpoint on the INT3/O, and lack of re-injection also
breaks nested virtualization, e.g. if L1 injects a software interrupt and
vectoring the injected interrupt encounters an exception that is
intercepted by L0 but not L1.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
arch/x86/kvm/svm/svm.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ecc828d6921e..00b1399681d1 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3425,14 +3425,24 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
static void svm_inject_irq(struct kvm_vcpu *vcpu)
struct vcpu_svm *svm = to_svm(vcpu);
+ u32 type;
+ if (vcpu->arch.interrupt.soft) {

It should be possible to inject soft interrupts even with GIF masked,
looked at the relevant code at patch 3 from my series [1].